Radial piston machine intended for use as a pump, compressor or motor

ABSTRACT

A radial piston machine having a valve slide shaft upon which is journalled a rotor with radial cylinders within which pistons are movable inwards/outwards relative to said shaft, and around the rotor a ring arranged for rotation about an axis excentric to the slide shaft. Rollers are arranged between the pistons&#39;&#39; outer end faces and a roller race on the inside of said ring serving to transmit motion between the ring and rotor during rolling. Holder elements having fixed stop edges are provided on the rotor end face sides on either side of each piston, thereby limiting the movements of the rollers on the piston end faces. The rollers also have axial guide pins fitting into grooves in end faces attached to the ring, these pins holding the rollers in contact with or near the roller race on the ring.

United States Patent 1191 Gransten Apr. 30, 1974 RADIAL PISTON MACHINE INTENDED I Y 2,977,891 4/1961 Bishop 91/485 FOR USE AS A PUMP, COMPRESSOR 0R 3,583,286 6/1971 Chiappulini 91/491 MOTOR Inventor: Gunnar Lennart Gransten,

Saltsjo-Boo, Sweden Assignee: AB Hagglund & Soner,

Ornskoldsvik, Sweden Filed: Dec. 11, 1972 Appl, No.: 314,239

Primary ExaminerWilliam L. Freeh Attorney, Agent, or Firm-Young and Thompson [57] ABSTRACT A radial piston machine having a valve slide'shaft upon which is journalled a rotor with radial cylinders within which pistons are movable inwards/outwards relative to said shaft, and around the rotor a ring arranged for rotation about an axis excentric to the slide shaft. Rollers are arranged between the pistons outer [30] Foreign Application Priority Data Dec. 22 1971 Sweden 16480/71 end faces and a mile race on the inside of said ring serving to transmit motion between the ring and rotor [52 U.S. Cl. 91/496 during H1der elements having fixed [51] Int. Cl. F0lb 13/06, edges are provided on the rotor end face Sides on [58] Field of Search 91/491, 492, 496; 497' Side of eachi'piston, thereby limiting the movements of the rollers on the piston end faces. The 1'01- [56] References Cited lers also have axial guide pins fitting into grooves in UNITED STATES PATENTS end faces attached to the ring, these pins holding the rollersin contact with or near the roller race on the 3,106,167 10/1963 Bjorklund et al. 91/497 ring. 2,115,296 4/1938 Banedek 91/492 2,103,314 12/1937 Banedek 91/496 SClaims, 3 Drawing Figures 18 g 17 1s j 21 r" 4-i g 1 2 z 26 7 25 5 RADIAL PISTON MACHINE INTENDED FOR USE AS A PUMP, COMPRESSOR OR MOTOR The present invention relates to a radial piston machine intended for use as a pump, compressor or motor, with a centrally arranged fixed valve slide shaft upon which is journalled a rotor with radial cylinders within which are pistons movable inwards and outwards relative to the slide shaft, and around the rotor a rotor ring arranged for rotation about an axis excentric to the slide shaft, and roller elements arranged between the pistons outer end faces and a roller path (race) on the inside of the rotor ring serving to transmit motion between the rotor ring and the rotor during rolling, caused by the excentricity, to and fro on roller paths (races) formed on the said piston end faces.

A rotary machine of the aforesaid radial piston type is known to the art from, for example, Swedish Pat. No. 325,479. A feature peculiar to this type of rotary machine is that no external torque is either taken from or put into the machines rotor. Instead, the torque is transferred via the rotor ring.

- In the abovementioned radial piston machine the roller elements roll to and fro on the piston end faces over a distance corresponding to the excentricity. To each angular position of an individual piston in the machine there corresponds a definite roller position determined by the geometry of the machine and by the current load conditions obtaining. The rollers are held in their seatings by contact pressure against the rotor ring on one side and the piston end faces on the other. The main parameters governing the machines geometry of motion are the excentricity, diameter of rotor ring and diameter of rollers. The loading conditions are determined by the ratio between the piston forces obtaining in that part of the machine where the pressure medium (working medium) is at a high pressure level and the corresponding piston forces in the part where the pressure level is low. By piston forces we here mean the hydraulic forces and forces of piston resilience operative in the cylinder chamber plus the forces of intertia in'the form of centrifugal forces. All these forces are directioned so as to assist in increasing the contact forces on the rollers. The term hydraulic force will henceforth be deemed to 'cover not only liquid pressure but also gas pressure in possible applications where the working medium is a gas. But acting on the pistons is yet another force determined by the hydraulic pressure and obtaining in the machine casing surrounding the rotor and slide shaft. This hydraulic pressure, hereinafter called the draining pressure, arises through flow of pressure medium into the machine casing through split seals between pistons and cylinders and between rotor and slide shaft. The pressure level is there determined by the inflow and by the restrictions in the way of outflow from the machine casing. Another efi'ect experienced in certain conditions is displacement variations of rotor plus pistons due to torsional vibrations. The force exerted on the pistons due to the drainage pressure acts in opposition to the forces-previously mentioned and thus tends to reduce the contact forces on the rollers. The margins for said contact forces thus depend on the drainage pressure and are in general least for the pistons/rollers working on the machines LP side and especially on the outer end faces of these pistons where the forces of piston resilience are least. If the margins are reduced to such an extent that the contact forces are nullified, the rollers may be caused to shift from their geometrically appointed positions under the action of accelerations.

The purpose of the present invention is to allow operation with a higher drainage pressure than hitherto, i.e., with smaller contact force margins, while at the same time fully ensuring proper positioning of the roller with respect to the pistons end face. The invention likewise aims to allow application of so high a drainage pressure that the to and fro motion of the pistons is eliminated with the result that the machines pump action ceases or, in other words, disengagement occurs.

In a type of radial piston machine known to the art from German Pat. No. 953,223 the problem of positioning the roller elements with respect to' the corresponding pistons has been partly solved by providing the piston outer end faces with lips that limit the movement of the rollers in the circumferential direction. However, in this case the lips have not only the task of limiting the movement of the rollers but also a primarily driving fuction (between the rotor and the surrounding casing) in combination with the rollers. However, this arrangement does not ensure that the roller elements maintain their positioning with respect to the corresponding pistons in the event of the pressure in the casing exceeding certain values.

According to the present invention, the aforesaid problem is resolved by providing the machine with holder elements that hold the roller elements in position before the piston end faces, in contact with or near the roller path (race) on the rotor ring, even if the pistons are so far within the cylinders that contact between the roller elements and pistonend-faces is lost.

The most important features of the radial piston machine designed according to the present invention are:

l. Full reliability as regards positioning of the roller with respect to the associated piston end face in the event of complete cessation of the contact forces and removal of the piston from the roller;

2. The holder elements need have no moving parts that would suffer wear in normal continuous operation, only liquid friction being involved;

3. The dimensions of a machine (both radial and axial) with given displacement need not be increased in consequence of the design features according to the invention and are in fact comparable to those of a machine without the said design features.

ln a preferred embodiment of the radial piston machine according to the invention, the holder elements include fixed stop devices on the rotor face sides, which stop devices have bearing edges on either side of each piston serving to limit movement of the roller elements on the piston end faces. The roller elements are in turn preferably provided with axial guide pins fitting into circumjacent grooves located in end faces joined to'the rotor ring. The roller elements are further preferably designed as rollers with end flanges coacting with circumscribing guide surfaces on the rotor ring.

In a particularly advantageous embodiment of the radial piston machine according to the inventionthe terminal positions of the roller element on the piston end face is determined by coaction between the end flanges of the roller element and the edges of the stop devices, the stop point in each outer position being so located that in such position the contact force between roller i element and piston gives rise to a moment about the centerline of the slide shaft which moment tendsto shift the roller element from the outer position further inwards on the pistons end face.

In short, one can say that the characteristic feature of the embodiments, as ascertained in the claims, is that the position of the roller relative to the pistons outer end face (hereinafter called the piston roller path or race) is determined partly by coaction between the axial guide pins of the roller elements and the circumjacent grooves in the rotor ring faces, whereby the rollers are prevented from shifting from the rotor rings contact surface under the action of radial accelerations, and partly by the stop devices fitted on the rotor faces serving to prevent the rollers from leaving the zone in theway of the piston roller path (race) and the cylinder opening under the action of tangential accelerations. As already mentioned, the need for special positioning of the roller elements arises only in cases where the contact forces on the rollers are nullified.

Further advantages and features of the radial piston machine according to the invention will be made apparent from the following detailed description with reference to the exemplary embodiment illustrated in the drawing attached. FIG. 1 shows a radial section of the machine through one of its cylinders, FIG. 2 is a view of the machine seen from the end of the slide shaft with one end of thecasing removed, and FIG. 3 illustrates schematically the design principle adopted in order to minimize the effect of the holder elements on the machines overall dimensions.

FIG. 1 illustrates the construction of the machine. The slide shaft 1 carries the hydrostatically journalled rotor 2 as well as the machine casing comprising the rotor ring 3 and end faces 4, 5. The machine casing is excentrically journalled with respect to the rotor by means of roller bearings (Sand 7 at either end of the slide shaft. The end plane 8 of the slide shaft is designed as a mechanical and hydraulic coupling plane for the machine. From this plane are led the main axial ducts to the two slide ports and 9 for the machines HP and LP sides, respectively. Ports 9 and 10 communicate cyclically with the several cylinder chambers. From end plane 8 there is also led a further duct 32 which is in direct communication with the interior of the machine casing. It is through this duct that the leakage flow is drained.

In the cylinder chamber 11 the piston 12 moves to and fro in consequence of the bearing point on the rotor ring varying its distance from the rotors axial centerline 30 (FIG. 2) during the course of rotation, depending in turn on the excentricity distance between the said axial centerline and the rotor rings centerline axis 27. The plane 13, in which both central axes 30 and 27 lie, is called the plane of excentricity. This plane has a dual functional significance: firstly it is the plane in which the pistons both turning points in the cylinder chambers are reached, and secondly it is the plane which divides the machines piston/cylinder equipment into one side woring with working medium at a low pressure level and one side working with the working medium at high pressure.

Piston 12 is loaded in the cylinder chamber by two concentric compression springs which in the exemplary embodiment here illustrated consist of two helical springs 14 and 15 of opposite lays. The reason for having two springs is firstly that by this means the maximum possible spring force can be got into the space available and secondly the risk is minimized of the piston tending to twist in the cylinder chamber in the event of contact with the roller being lost. As is apparent from the foregoing, the main task of these springs is to provide a mechanical back-up force on piston 12 in addition to the hydraulic and inertial forces that act upon it. Since the hydraulic forces may assume values ranging from complete vacuum (in the pressure medium) to full working pressure, depending inter alia on the compressibility of the pressure medium and pressure fluctuations caused thereby in the hydraulic system, it is easy to see why there is a need for the aforesaid superposed spring forces in order to maintain, in most operating conditions, positive contact forces between piston 12, roller 16 and rotor ring 3.

The cylindrical roller 16 is provided at its ends with concentric flanges 17 and 18 which are slightly tapered towards the roller surface and coact with corresponding chamfers on the inner edges of the rotor ring. One function of these flanges is toguide the movement of the roller suchwise that its generatrices remain parallel to those of the rotor ring. 7

However, in the case of the present invention a further function has been assigned to these flanges, namely that of forming stops for tangential positioning of the roller relative. to the piston roller path or race.

According to the invention, radial limitation of the rollers movement is secured by contriving that, in the zone axially beyond the said flanges, the roller is designed with cylindrical pins 19 and 20 that engage in the mutually concentric grooves 21 and 22 on the inside of end faces 5 and 4, respectively.

Regarding tangential positioning of the roller, it is inconvenient, on grounds of function and space alike, to use the previously known solution whereby the piston end faces are provided with stops for limiting the rollers rolling movement. That this is so in the radial piston machine according to the invention, with its special method of operation, is due to the fact that the machine is adapted for such a large excentricity in relation to the piston diameter that the rollers tangency point in certain angular postures lies outside the pistons boundary gener'atrix (see angular posture a 270 in FIG. 2). Since during about half a revolution (when angle a is between 90 and 270) the'piston end faces withdraw into the cylinders within the rotors external diameter, a hypothetical roll locking arrangement of this sort would drastically increase the radial size of the machine.

Nor is the limiting function of the cylinder openings divergent planes 28 and 29 in the rotor satisfactory in combination only with pins 19, 20 and grooves 21, 22. These divergent planes have in fact a tangential limiting effect only when angle a is between about and Another theoretically conceivable solution would be to fit, say on either side of the piston and parallel to its centerline, radially movable pins, spring-loaded outwards, in combination with the abovementioned pins and grooves. But in the vast majority of cases such a solution would be clearly inconvenient. In the first place such pins would have to move, in one revolution of the machine, over a distance equivalent to twice the excentricity, i.e. at the outer turning position (a 0) and equally large part of the pin would have to project from an associated guide hole in the rotor. Moreover, a certain portion of the pin must remain 'within the guide hole lest the lateral reaction forces become so great that. jamming occurs. At the inner turning point (a 180) the guide hole would have to be deep enough to accommodate the whole length of the pins plus possibly a helical push-out spring. However, in most cases considerations of space would make such an arrangement impracticable in the limited sectors available between the pistons and the centerline plane of the rotor. In the second place, such a solution, assuming it were possible from the standpoint of availabe space, would mean an unsatisfactory service life because of the unavoidable wear.

In the present invention this awkward problem has been otherwise solved, namely by fitting fixed roller holder plates 25 and 26 on the rotor at equal distances from the rotors plane of symmetry through the cylinder axis and with a distance between them equal to that between the centerline planes of roller flanges 17 and 1-8. The radial extent of plates 25 and 26 is bounded by a circle having the centre of the rotor as its centre, and with a radius such that at the inner turning position (a 180) these plates move down, with minimum radial play, into grooves 23 and 24 between the end faces and edge surfaces of the rotor ring. At the outer turning position ('0: 0) the play is increased accordingly by twice the excentricity (see also FIG. 3).

Around each cylinder mouth the plates form a symmetrical opening within which the roller flanges can freely follow the rollers normal motions without coming into contact with the plate edges 31. Normal motions are here deemed to be:

The movement cycle performed by the roller over the piston roller path (race) during one revolution of the machine when the latter is off-load, i.e. with a set of rollers fully symmetrical with respect to the plane of excentricity 13 when a pair of cylinders passes this plane;

The rolling distance, determined by the rotors twist relative to the machine casing in the case of maximum torque loading;

A certain fixed rolling distance corresponding to the admissible torsional vibrations of certain amplitude about the loaded equilibrium position.

. By summating the three abovementioned movement quantities, and bearing in mind that the machine is reversible, we arrive at .the width of the roller holder plate openings.

For reasons already mentioned, the roller plate holders have their least margins at the pistons outer turning position (0: =0") with a view to driving by the roller flanges. Seeing that the width of the roller holder opening is fixed according to what has been said hereinover, the only way to minimize the margins is by varying the roller flange diameter and the outer limiting diameter of the roller holder plates. The rollers own diameter is given. The practical criterion for determining the other two said diameters is apparent from FIG. 3. This assumes hypothetically that the piston before the outer turning position has lost contact with the roller at the same time as the equilibrium of moments on the rotor is for some reason or other disturbed so that the rotor is immediately turned forward to the position where the corner of roller holder plate 25 has reached the plane of excentricity13. It is further assumed that at this point in time the rollers flanges have borne hard up on the corner of the roller holder plate, as shown in FIG.

3. Since the cylinder chamber is now in communication with the pressure medium at the high pressure level, the contact force R (between roller and piston) will aiso be determined by that pressure and may consequently assume high values. The product of the contact force R and its lever arm distance from the centre of the rotor determines the pistons contribution of moment to the rotors moment equilibrium. As can be seen from FIG. 3 this moment contribution is such that it tries to turn the rotor back relative to the machine casing and also spontaneously to reset the roller to its correct positioning on the piston roller path. The theoretical limiting case for both the aforesaid diameters is determined by the condition obtaining when the roller bears partly on the corners of the stop surfaces (plate edges 31) and partly on the edge of the piston in such a manner that sliding in some contact point just begins, when the roller must again roll onto the piston roller path, i.e. roller race. To go to such lengths for practical design is out of the question for several reasons, among them unacceptably large surface pressures. Consequently, dimensioningof the roller holder plate and roller flange diameters is so chosen that the direction of the contact force R shall, in the aforesaid hypthetical case, be essentially parallel to the longitudinal axis of symmetry of the corresponding cylinder. The margins thereby secured are perfectly adequate for the rollers driving as has incidentally been confirmed by experiment. This is so regardless of whether the operating conditions envisage temporary easing of the pistons or their intentional pressing in.

What is claimed is:

l. A radial piston machine, intended for use as a pump, compressor or motor, with a centrally arranged fixed valve slide shaft upon which is journalled a rotor with radial cylinders within which are pistons movable inwards and outwards relative to the slide shaft, and around the rotor a rotor ring arranged for rotation about an axis eccentric to the slide shaft, and roller elements arranged between the pistons outer end faces and a roller path on the inside of the rotor ring serving to transmit motion between the rotor ring and the rotor during rolling, caused by the eccentricity, to and fro on roller paths formed on the said piston end faces, characterized by provision of holder elements whichho'ld the roller elements in position for the piston end faces, in contact with or near the roller path on the rotor ring, even if the pistons are withdrawn so far into their cylinders that contact between the roller elements and the piston end faces is lost, the roller elements having axial guide pins fitting into circumjacent grooves located in end faces jointed to the rotor ring.

2. A radial piston machine according to claim 1, characterized in that the holder elements include, on the rotor end face sides, fixed stop devices having bearing edges on either side of each piston, serving to limit the movements of the roller elements on the piston end faces.

3. A radial piston machine according to claim 1, characterized in that the roller elements are formed as rollers having end flanges which coact with circumjacent guide surfaces on the rotor ring.

4. A radial piston machine, intended for use as a pump, compressor or motor, with a centrally arranged fixed valve slide shaft upon which is journalled a rotor with radial cylinders within which are pistons movable inwards and outwards relative to the slide shaft, and

around the rotor a rotor ring arranged for rotation about an axis eccentric to the slide shaft, and roller elements arranged between the pistons outer end faces and a roller path on the inside of the rotor ring serving to transmit motion between the rotor ring and the rotor during rolling, caused by the eccentricity, to and fro on roller paths formed on the said piston end faces, characterized by provision of holder elements which hold the roller elements in position for the piston end faces, in contact'with or near the roller path on the rotor ring, even if the pistons are withdrawn so far into their cylinfaces. 

1. A radial piston machine, intended for use as a pump, compressor or motor, with a centrally arranged fixed valve slide shaft upon which is journalled a rotor with radial cylinders within which are pistons movable inwards and outwards relative to the slide shaft, and around the rotor a rotor ring arranged for rotation about an axis eccentric to the slide shaft, and roller elements arranged between the pistons'' outer end faces and a roller path on the inside of the rotor ring serving to transmit motion between the rotor ring and the rotor during rolling, caused by the eccentricity, to and fro on roller paths formed on the said piston end faces, characterized by provision of holder elements which hold the roller elements in position for the piston end faces, in contact with or near the roller path on the rotor ring, even if the pistons are withdrawn so far into their cylinders that contact between the roller elements and the piston end faces is lost, the roller elements having axial guide pins fitting into circumjacent grooves located in end faces jointed to the rotor ring.
 2. A radial piston machine according to claim 1, characterized in that the holder elements include, on the rotor end face sides, fixed stop devices having bearing edges on either side of each piston, serving to limit the movements of the roller elements on the piston end faces.
 3. A radial piston machine according to claim 1, characterized in that the roller elements are formed as rollers having end flanges which coact with circumjacent guide surfaces on the rotor ring.
 4. A radial piston machine, intended for use as a pump, compressor or motor, with a centrally arranged fixed valve slide shaft upon which is journalled a rotor with radial cylinders within which are pistons movable inwards and outwards relative to the slide shaft, and around the rotor a rotor ring arranged for rotation about an axis eccentric to the slide shaft, and roller elements arranged between the pistons'' outer end faces and a roller path on the inside of the rotor ring serving to transmit motion between the rotor ring and the rotor during rolling, caused by the eccentricity, to and fro on roller paths formed on the said piston end faces, characterized by provision of holder elements which hold the roller elements in position for the piston end faces, in contact with or near the roller path on the rotor ring, even if the pistons are withdrawn so far into their cylinders that contact between the roller elements and the piston end faces is lost, the roller elements being formed as rollers having end flanges which coact with circumjacent guide surfaces on the rotor ring.
 5. A radial piston machine according to claim 4, characterized in that the holder elements include, on the rotor end face sides, fixed stop devices having bearing edges on either side of each piston, serving to limit the movements of the roller elements on the piston end faces. 